As we often say you can do a lot with an Arduino and the following project is a great example of this. Arduino forum member "rediculum" is working on a staging box to control a 20mW laser that will generate various lighting effects. It uses a system of servo-controlled mirrors to alter the laser reflection and thus the resulting patterns, and after final construction will end up cheaper than a commercial unit. Here's an example of the current work in action:
It's a work in progress, however the project is being documented very well, and you can follow to find the results from here. And for more, we're on twitter and Google+, so follow us for news and product updates as well.
To get started with your own projects based on a miniature Arduino-compatible - look no further than the Freetronics LeoStick. Apart from being one of the smallest Arduino-compatibles on the market with USB, it also has an onboard RGB LED and piezo for sound and knock detection: